Imaging of Protein Secretion from a Single Cell Using Plasmonic Substrates

Detecting, imaging, and monitoring cell function on a single cell basis is very important in the field of immunology research where many molecules are secreted from cells in response to external stimuli including immunization. Here we introduce substrates with plasmonic nanoparticles and fluorescence microscopy as promising imaging methods for studies on molecular processes controlling cell behavior, particularly secretion of cytokines. We developed unique composition of silver and silica layers of plasmonic nanostructures which resulted in fluorescence enhancement of more than 200-fold for ensemble of molecules in the immunoassay. For the proof of concept demonstration, we used primary mouse macrophages and imaged tumor necrosis alpha (TNF-α) secretion after stimulation of the cells with lipopolysaccharide (LPS). We demonstrate that metal-enhanced fluorescence assay provides imaging capability detection of cytokine secretion from a single cell without extensive biochemical procedures as required with standard methods. In addition it is demonstrated that cell viability can be controlled during secretion.